JP2001518737A - CDMA communication system improved by polarization - Google Patents

Abstract

The present invention is a novel and improved method and apparatus for transmitting and receiving code division multiple access (CDMA) signals. In a described embodiment of the invention, the radio frequency (RF) signals are received through a first polarization RF unit and a second polarization RF unit generating right slant samples and left slant samples. The right slant samples and the left slant samples are each searched and multipath processed independently and the resulting sets of soft decision data combined and decoded. In a preferred embodiment of the invention, right slant and left slant instances of the signal are generated and transmitted to increase the likelihood of differently polarized instances of the signal being available at the receive system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to wireless telecommunications. In particular, the present invention relates to code division multiple access (C
The present invention relates to a method and apparatus for utilizing signal polarization to enhance transmission and reception functions of a signal processed using a DMA (DMA) signal.

[0002]

[Prior art]

The IS-95 standard defines a code division multiple access (CDMA) air interface that provides efficient and robust cellular telephone services. IS-
The 95 standard is the Telecommunication Industry Association (TIA).
n) and cellular phones and base stations manufactured by different manufacturers,
You can now communicate with each other. FIG. 1 shows a cellular system configured according to the IS-95 standard. Further, a cellular telephone system configured substantially in accordance with IS-95 is disclosed in U.S. Pat. No. 5,103,459 (Title of Invention: System and Metho).
d for Generating Signal Waveforms in a CDMA Cellular Telephone System), which is assigned to the same assignee as the present application and incorporated herein by reference.

[0003] Modulating a plurality of user signals using a set of pseudo-random codes (PN codes) before a set of user signals is up-converted to a radio frequency (RF) band by CDMA signal processing. This enables transmission in the same RF frequency band. This PN code is used to modulate and demodulate the user signal in each of the transmission and reception processes. A first advantage of using CDMA signal processing is that adjacent base stations can use the same RF band, which increases the frequency utilization efficiency of a cellular telephone system using the available RF band.

Another advantage of CDMA is that it allows for multipath signal processing. Multipath signal processing is the individual processing of different copies of the same transmission signal caused by reflection and other multipath phenomena. Generally, various copies of the transmitted signal are processed by a set of demodulators, each demodulator being synchronized to the state of the PN code for the signal. During processing of certain multipath signals, other asynchronous multipath signals are detected as background noise or interference. As each multipath signal is processed, the resulting "soft decision" data is generally combined into a single data set, which is decoded.

[0005]

[Problems to be solved by the invention]

While the use of multipath signal processing improves the performance of a CDMA receive processing system, interference of other multipath signals that occurs during processing of a particular multipath signal is still undesirable. This interference may cause fading, which may reduce the total number of communications that can be performed by a particular base station. Providing a method and apparatus for reducing the degree of interference of a set of inter-multipath signals further improves the performance of the multipath received signal system. The object of the present invention is in this respect, in addition to the object described below.

[0006]

[Means for Solving the Problems]

The present invention uses code polarization for code division multiple access (CD).
MA) A new and improved method and apparatus for improving transmission and reception signal processing using signals. In one embodiment, the right-handed and left-handed polarizations of the signal are transmitted using separate antennas, increasing the likelihood that differently polarized signals will be available at the receiving system, and with one delay. To provide additional diversity. The receiving system consists of a single polarized antenna and a diversity receiver that selects the best instance of the received signal, which typically depends on the polarization direction and antenna direction of those signals. I have. In another embodiment, the receiving system comprises two antennas having different polarization characteristics and increasing the possibility of improving the quality of the received signal.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention is a new and improved method and apparatus for improving transmission and reception signal processing using code division multiple access (CDMA) signals using the polarization of the signal. In the following description, the present invention is implemented in a CDMA cellular telephone system operating according to the IS-95 standard. The present invention is particularly suited for the operation of cellular telephone systems operating according to the IS-95 standard, but is not intended for communications satellite systems or point-to-point
It can also be applied to other wireless communication systems such as nt-to-point communication systems, as well as rake receivers such as wired systems using sinusoidal signals and coaxial cable communication systems.

FIG. 2 is a simplified block diagram of a portion of a cellular telephone system constructed in accordance with one embodiment of the present invention. Base stations 22 and 22a are connected to a base station controller 24, which is connected to a telephone switching network (PSTN). PSTN is a common wired telephone network. As shown, base station 22 is transmitting RF signals to subscriber unit 20 for communication. Typically, the subscriber unit 20 transmits an RF signal to the base station 22, but this transmission has been omitted for simplicity.

In a preferred embodiment of the present invention, base station 22 includes right tilt signal 60 and left tilt signal 6
Two orthogonally polarized forward link signals, denoted as 2, are transmitted from antenna systems 54a and 54b. In this embodiment, these signals are
And corresponds to a digital signal generated by two RF subsystems 52a and 52b and received from a digital processing system (DPS) 53.
The DPS 53 receives the data transmitted from the BSC 44.

[0010] A delay 50 is connected to the RF subsystem 52a. The delay 50 adds a delay to the outgoing left tilt signal 62 and provides time diversity. This amount of delay is one bit or more than "chip" of the PN code used at the time of modulation and demodulation, and is preferably 2 to 3 chips. As those skilled in the art will appreciate, DP
There are various signal delay insertion methods including the delay insertion in S53. However, since it is necessary only to generate one digital signal, it is desirable to provide a delay after the processing performed by the DPS 53.

As is known in the art, a radio frequency signal can be subjected to various orthogonal polarization processes, including left and right tilt polarizations that are tilted 45 degrees from vertical. In addition, various polarizations are known, including horizontal and vertical linear polarization, or right-handed circuit (RHC) and left-handed circuit (LHC) polarization, and their use is also included in the present invention.

In one embodiment, right tilt signal 60 and left tilt signal 62 are transmitted in different directions. For example, antenna 54a is oriented slightly differently than antenna 54b. Preferably, the difference in direction is small so that the two signals are received at the same location via different multipath environments. This increases the diversity of the signal source. Alternatively, this direction may be further substantially changed. For example, subsystem 5
2a and 52b may be located at different locations with antennas 54a and 54b. This has the effect of creating different cells with different polarizations. As the subscriber unit moves from one cell to the next, the polarization of the received signal changes. Of course, the antennas are pointing in the same direction.

As shown in FIG. 2, the right tilt signal 60 is reflected on a tree 61 and is reflected on a tree 61.
a, and the left tilt signal 62 is reflected on the building 63 to generate a multipath 62a. As is known in the art, reflection changes or adds polarization to a non-polarized signal. The subscriber unit 20 receives signals 60, 60a, 62 and 62
a, and performs reception demodulation to extract transmission data.

FIG. 3 is a block diagram showing a reception processing unit of the subscriber unit 20 configured according to one embodiment of the present invention. The antenna system 70 is connected to an RF receiver 74,
The RF receiver 74 includes demodulators 80a-c, and further includes a searcher and controller 78.
It is connected to the. Demodulators 80 a-c are also connected to searcher and controller 78 and combiner 82. Although three demodulators 80 are shown, the use of other numbers of demodulators, including four, is also included in the present invention.

In operation, antenna system 70 receives left tilt and right tilt RF signals from base station 22. The RF receiver filters, frequency downconverts, and digitizes these signals to generate samples 86. The searcher and control system 97, 80 receives the sample 86 and performs an iterative offset search using the PN code used to modulate the signal, and the arrival time of each of the signals 60, 60a, 62 and 62 in FIG. Judge. Once the arrival times of the signals 60, 60a, 62 and 62 have been determined, the searcher and control system 7890 converts the signals 60, 60a, 62 and 62 to the respective arrival samples 86 or 88 with the right slope sample 86 or the left slope sample 88, respectively. At time, the demodulators 80a-c are instructed to process using the control interface 92.

In the preferred embodiment, demodulators 80a-c include PN spreading codes and Walsh
sh) Demodulate the sample using the channel code. These codes are constructed and generated according to the IS-95 standard and the respective arrival times (offsets) involved. The demodulators 80a-c also perform time tracking to adjust for variations in each arrival time. Demodulation by demodulators 80 a-c generates soft decision data received by combiner 82. A combiner 82 combines the soft decision data 94a-c to generate summed soft decision data, which is received by a decoder (not shown). The decoder performs soft decision decoding to generate hard decision data 99,
This data 99 can be used for further processing such as data manipulation or acoustic tones. Various decoding methods are known, including coding in trellis or Viterbi, and are applicable to the present invention.

By using differently polarized RF receivers, the various received signals can be separated from each other before demodulation, thereby reducing the degree of interference with each other. Typically, the antenna system 70 has a shape for separating polarization signals different from each other and a polarization reception characteristic determined by its direction. As the direction changes, the characteristics of the polarization reception also change, providing signal diversity over time. This improves the processing performance of the subscriber unit 20 and the call processing performance of the corresponding cellular telephone system. This improved call handling capability is used to increase the number of telephone calls that can be made, given certain conditions.

FIG. 45 is a block diagram showing a reception processing unit of the subscriber unit 20 configured according to another embodiment of the present invention. Right tilt antenna system 270 and left tilt antenna system 272 receive an RF signal, which is transmitted to RF receivers 274 and 276.
Provided to RF receivers 274 and 276 are connected to demodulators 280a-c and searcher and controller 278. Demodulators 280a-c are connected to searcher and controller 278 and combiner 282. Three demodulators 28
Although zero is shown, the use of four or more demodulators is also included in the invention.
Although shown as right-tilt and left-tilt antenna systems 270 and 272, the typical polarization of the subscriber unit changes the absolute polarization of the antenna system, but the relative polarization. Does not change.

In operation, right tilt antenna system 270 receives signals having right tilt polarization, and left tilt antenna system 272 and receiver 274 filter, frequency downconvert and digitize the signals, 286 is generated. Similarly, left tilt antenna system 272 performs polarization filtering of the RF signals, and receiver 276 frequency filters, downconverts, and digitizes the signals, and left tilt samples 288
Occurs. Various methods and antennas for performing polarization reception are known. Therefore,
Right-tilt sample 286 includes only signals with right-tilt components, so that interference due to orthogonally polarized signals is removed. Similarly, left tilt sample 288 includes only signals having a left tilt component, so that interference from other orthogonally polarized signals is removed.

The searcher 290 receives the right-tilt sample 286 and the left-tilt sample, repeatedly performs an offset search using the PN code used to modulate the signal, and obtains signals 60, 60a, 62 and 62a of FIG. Judge each arrival time. Once the arrival times of the signals 60, 60a, 62 and 62a have been determined, the searcher 290
Configures demodulators 280a-c to process signals 60, 60a, 62 and 62a at either corresponding arrival time using control interface 272 at either right sloped sample 286 or left sloped sample 88. In a preferred embodiment,
Demodulators 280a-c demodulate the samples using PN spreading codes and Walsh channel codes that are constructed and generated according to the IS-95 standard and corresponding respective arrival times (offsets). In addition, demodulators 280a-c perform time tracking and adjust for variations in each arrival time.

The demodulation performed by demodulators 280 a-c generates soft decision data and is received by combiner 282. Combiner 282 combines the soft decision data to generate summed soft decision data, which is decoded by a decoder (not shown). The decoder codes the soft decision data and generates hard decision data, which is used for further processing such as data manipulation and generation of acoustic tones. Various decoding methods are known, including trellis or Viterbi decoding, and are applicable to the present invention.

By using differently polarized RF antennas, various received signals can be separated from each other before demodulation, thereby reducing the degree of interference with each other. Furthermore, by using two antennas with different polarizations, the most accessible signals can be received, identified and processed independently, thereby improving the average signal quality. This improves the processing performance of the subscriber unit 20 and the call processing performance of the corresponding cellular telephone system. This improved call handling capability is utilized to increase the number of telephone calls that can be made in a given condition.

FIG. 2 is a simplified block diagram illustrating a portion of a cellular telephone system configured in accordance with another embodiment of the present invention. Base station 22 is connected to a base station controller 24, which is connected to a telephone switching network (PSTN). P
STN is a conventional wired telephone network. As shown, subscriber unit 20 transmits RF signals to subscriber unit 20 for communication.

The subscriber unit 20 applies two orthogonally polarized forward link signals, denoted as right tilt signal 360 and left tilt signal 360 b, to antenna systems 362 and 364.
Arising from These signals are signals transmitted by two separate antennas that are part of the subscriber unit 20 in response to digital signals received from the digital unit 365. This data is received from an external source such as digital audio.

[0025] Delay 350 is connected to RF unit 352b. The delay 350 adds a delay to the externally transmitted left tilt signal 362 to provide time diversity.
The magnitude of the delay is at least one bit or chip of the PN code used for modulation and demodulation, and is preferably a time of two to three chips. As will be appreciated by those skilled in the art, there are a variety of ways to add delay to the signal, including the insertion of delay by digital unit 353. However, a delay is required after the processing performed by the digital unit 353, since a delay is necessary for the generation of only one instance of the digital signal.

As described with reference to FIG. 2, the right tilt signal 360a and the left tilt signal 360b are transmitted in different directions. For example, antenna 364 is oriented in a slightly different direction from antenna 362. Preferably, the difference in direction is small so that the two signals are received at the same location via different multipath conditions. This improves the diversity of the signal source.

As shown in FIG. 5, the right tilt signal 364 reflects the tree 61 and the multipath signal 3
62a, the left tilt signal 362 reflects the building 63 and the multipath signal 362b
Occurs. As is known in the art, reflection deforms an already polarized signal or adds polarization to an unpolarized signal. Base station 22 receives signals 360, 360a, 36
2 and 362a are received and demodulated to extract transmission data. In one embodiment of the present invention, base station 22 transmits signals 360, 360a, 362 and 362a,
Some of the resulting multipath is received via an antenna system with specific polarization to filter. FIG. 6 is a block diagram illustrating a part of a reception processing system of a base station 22 configured to communicate with a subscriber unit 20 according to another embodiment of the present invention. At base station 22, a cell site modem (CSM) 84 is shown connected to the antenna system. This antenna system is a right tilt antenna 17
0 and left tilt antenna 172 and RF receivers 174 and 176. Typically, the base station receives a set of signals, such as signals 360, 360a, 362, 362a of FIG. As shown, the base station receives three instances or occurrences of the RF signal transmitted from the subscriber unit 20. Example 60 is received on a direct path. Another example 162 reflects tree 161. The third example 164 is a building 163
Is reflected. Further, other signals are transmitted from other subscriber units 20 and received at antennas 170 and 172.

The signal received at right tilt antenna 170 is the signal to receiver 174, which filters, delay converts and digitizes the delayed signal. The signal received by left tilt antenna 172 is provided to a receiver 176, where it is filtered, frequency reduced, and digitized. The digitized signals from receivers 174 and 176 are provided to a cell site modem (CSM) 84 (partially shown) as well as other cell site modems (not shown) in the base station. The cell site modem 84 demodulates a set of multipath signals from a particular subscriber unit 20. A system and method for configuring each CSM on a single integrated circuit is described in US Pat. No. 5,654,979 (Title of Invention: Cell Site Demodulator Architecture for a Spread Spectrum Multi).
ple Access Communication System) and pending US application Ser. No. 08 / 316,177 (Title of Invention: Multipath Search Processor For A Spread Spectrum Mul).
tiple Access Communication System), which are assigned to the same assignee as the present invention.

[0029] Within CSM 84, the searcher and controller 178 receives the digitized signal and applies various time offsets to provide an associated spreading code to identify the multipath of the signal being processed. . Therefore, the searcher and the controller examine the inputs from antenna 170 and antenna 172 separately,
For a particular finger, determine which signal is producing the best result.
Once the multipath signal is identified, the searcher and controller 178 allocates one demodulator 180 and processes the multipath signal from the particular antenna determined to provide the best result. The demodulators 180a-c thus produced
Are combined by combiner 182, provided to a trellis or Viterbi decoder, and provided to the BSC.

By providing RF signals of different polarization characteristics at the transmitting system, the present invention improves the reception of multipath signals from the particular subscriber unit 20 at the receiving system. In particular, reflections and other phenomena that result in multipath transmission, including the occurrence of non-uniform polarization, often change the polarization characteristics of the signal. By providing a polarized antenna input, a multipath example of a differently polarized signal is filtered from other signals and thus does not interfere with other signals. The insertion of the delay reduces the likelihood that the signals will be destructively coupled and cause a fade phenomenon, and will also prevent interference.

Accordingly, the present invention provides a new and improved method and apparatus for transmitting and receiving code division multiple access (CDMA) signals. With the above description of the preferred embodiment, one skilled in the art can make and use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the principles defined herein apply to other embodiments without such inventive ideas. In particular, although the preferred configuration of the base station controller has been used to describe one embodiment of the present invention, it is applicable to base station controllers having alternative configurations. Accordingly, the present invention is not limited to the above embodiments, but has the broadest scope consistent with the principles and novel features disclosed herein.

[Brief description of the drawings]

FIG. 1 shows a cellular telephone system configured according to the IS-95 standard.

FIG. 2 is a block diagram showing a cellular telephone system configured according to a first embodiment of the present invention.

FIG. 3 is a block diagram showing a subscriber unit reception processing system configured according to a preferred embodiment of the present invention;

FIG. 4 is a block diagram illustrating a subscriber unit cellular telephone system configured in accordance with another embodiment of the present invention.

FIG. 5 is a block diagram showing a part of a subscriber unit transmission processing system configured according to an embodiment of the present invention.

FIG. 6 is a block diagram showing a part of a reception processing system in a base station configured according to a preferred embodiment of the present invention.

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Claims (13)

[Claims] 1. A method for transmitting information in a code division multiple access communication system, comprising: (a) transmitting a first polarization of the signal; and (b) transmitting a second polarization of the signal. A method comprising the steps of: 2. The method of claim 1, wherein said first polarization is orthogonal to said second polarization. 3. The method of claim 1, wherein the first polarization of the signal is transmitted in a different direction than the polarization of the signal. 4. The method of claim 1, wherein the first polarization of the signal has a different time offset with respect to the polarization of the signal. 5. The method of claim 1, wherein the first polarization of the signal is transmitted in a different direction and a different time offset with respect to the polarization of the signal. 6. A system for receiving a signal by a set of multi-pass copies, wherein a signal corresponding to the multi-pass copy is responsive to the set of multi-pass copies.
A first polarization receiving system for generating a first set of polarizations; a first system corresponding to the multipath copy in response to the set of multipath copies;
A second polarization receiving system for generating a set of second polarizations; and a set of first polarizations corresponding to the multipath copy and a set of second polarizations corresponding to the multipath copy. A first demodulation system for generating first soft-decision data, and a second soft-code responsive to a set of first polarizations for the multipath copy and a set of second polarizations for the multipath copy. A second demodulation system for generating decision data. 7. A searcher for identifying a time offset of a specific multipath copy in a set of first polarizations for the multipath copy and a set of second polarizations for the multipath copy. 7. The system of claim 6, wherein 8. The searcher further comprises: the first demodulation system and the second demodulation system for demodulating either a set of first polarizations for the multipath copy or a second set of polarizations for the multipath copy. 8. A system according to claim 7, wherein said second demodulation system is constituted.
The described system. 9. A system for transmitting a code division multiple access signal, comprising: a first radio frequency processing unit for transmitting a first polarization of the signal; and a second radio frequency for transmitting a second polarization of the signal. A system comprising: a processing unit. 10. The apparatus according to claim 9, wherein the first polarization is orthogonal to the second polarization.
The described system. 11. The first radio frequency processing unit transmits a first polarization of the signal in a first direction, and the second radio frequency processing unit transmits a second polarization of the signal to a second polarization. 10. The system according to claim 9, wherein the transmission is performed in the following directions. 12. The first radio frequency processing unit transmits a first polarization of the signal at a first time offset, and the second radio frequency processing unit transmits a second polarization of the signal for a second time. The system according to claim 9, wherein the transmission is performed with an offset. 13. The first radio frequency processing unit transmits a first polarization of the signal in a first time offset and a first direction, and the second radio frequency processing unit transmits a second polarization of the signal. The system of claim 9, wherein the wave is transmitted in a second time offset different from the first and in a second direction different from the first.